A wide variety of different portable wireless systems, such as cellular telephones, pagers and wireless personal digital assistants (PDAs), have been developed to enable users to communicate without being tied to a particular physical location. A cellular telephone network may be used by owners of such devices to wirelessly transmit voice and data communications to others connected to the network. Examples of cellular telephone networks include AMPS, D-AMPS, GSM, and IS-95 (CDMA). Such cellular telephone networks typically include a plurality of base stations each serving the cellular telephones within their geographic area, one or more base station controllers, and at least one mobile switching center. In general, a cellular telephone network covers a specific geographic area that typically is divided into cells (or regions). Each cell is allocated one or more voice/data channels or traffic/control channels, or both. A cellular telephone network usually has a broadcast channel on which all cellular telephones may obtain system information from the base stations or measure signal strength or signal quality, or both. A cellular telephone call is handed off from one cell (the serving cell) to a neighboring cell based upon the relative signal strength or quality between the cellular telephone and the base stations of the neighboring cells.
A number of different cellular telephone systems have been proposed. For example, many different multi-mode cellular telephones that switch between different types of telecommunication networks have been proposed. In one such system, a cellular telephone is configured to switch from a cellular telephone system to a wireline cordless telephone system when the cellular telephone is within range of a cordless telephone base station. Other cellular telephone systems allow an electronic appliance, such as a handheld computer or a laptop computer with an appropriate interface card, to transmit data over a wireless cellular telephone communication channel. The electronic appliance may be cellular-enabled or it may be coupled to a cellular telephone through a wired or wireless connection.
Recently, several low-power and low-cost wireless interfaces between electronic appliances have been proposed. For example, Bluetooth is a recently proposed universal wireless interface that operates within the ISM band (2.4-2.48 GHz) and allows portable electronic appliances to connect and communicate over short-range, ad hoc networks. A Bluetooth-enabled electronic appliance may communicate simultaneously with up to seven other similarly enabled electronic appliances to form a small local radio network. Among the applications that have been proposed for Bluetooth and other wireless interfaces are a three-in-one phone, an untethered computer, and a universal remote. A three-in-one could be used as a standard cellular phone, using a wireless carrier service. The phone also could be used as a cordless phone through a Bluetooth access point that is connected to a conventional wired telephone network. Finally, the phone could also be used as an intercom with direct point-to-point communications with similar devices, without involving any wireless carrier service. An untethered computer (e.g., a laptop computer) could be connected to a network such as the Internet via a Bluetooth modem access point. The modem access point would provide connectivity to the network in the normal fashion, such as over cellular telephony channels, telephone lines, cable or ISDN, but the computer would not be connected physically to the modem. A universal remote may be any Bluetooth device (e.g., a PDA or smartphone) that could be used to query and control other Bluetooth devices within communication range of the universal remote. Still other applications for such wireless interfaces have been proposed.